Grinding element, method for producing the grinding element and injection-molding tool for carrying out the method

ABSTRACT

A grinding element consists of a disk-shaped main body and blades formed as a unit therewith, wherein the main body and the blades are made of sintered hard material. An opening passing through the main body is arranged immediately in front of each blade with respect to a direction of rotation of the grinding element about a center axis. Each blade has a rake face that is partially cylindrical with a rake angle α=0° or partially conical with a rake angle α≠0°.

FIELD OF THE INVENTION

The invention relates to a grinding element, a method for producing a grinding element of this type and an injection-molding tool for producing a grinding element of this type according to the method.

BACKGROUND OF THE INVENTION

It is known to use ceramic abrasive particles, produced according to the so-called sol-gel method, in bound grinding elements or in coated abrasives. Furthermore, it is known to produce, by means of the sol-gel method, geometrically defined abrasive particles, having for instance a triangular shape. Grinding tools equipped therewith are more aggressive and more stable than conventional tools equipped with sol-gel abrasives.

SUMMARY OF THE INVENTION

It is the objective of the invention to provide a grinding element that is particularly easy to produce while providing excellent grinding properties and high stability.

This objective is achieved by a grinding element that consists of a disk-shaped main body and blades formed as a unit therewith, wherein the main body and the blades are made of sintered hard material; wherein—in relation to a direction of rotation of the grinding element about a center axis—each blade is immediately preceded by an opening passing through the main body; and wherein each blade has a rake face having a partially cylindrical shape with a rake angle α=0° or a partially conical shape with a rake angle α≠0°. In another aspect of the invention, a method for producing a grinding element according to the invention is provided, wherein an initial material is produced by kneading and mixing from an organic binding agent that becomes moldable when heated and hard material in the form of particles; wherein, in a subsequent step, a raw component of the grinding element is produced by injection molding; wherein, in a subsequent step, the binding agent is removed from the raw component; and wherein, in a subsequent step, the grinding element is formed from the raw component in a sintering process. In yet another aspect of the invention, an injection-molding tool for producing the grinding element according to the invention using the method according to the invention is provided, wherein two tool components are provided that define a molding space when the injection-molding tool is closed; wherein bolts are arranged on one tool component for molding the openings and the rake faces, the bolts engaging drill holes of the other tool component when the injection-molding tool is closed; and wherein recesses are formed in one tool component for molding the blades.

The essential feature is that the grinding element according to the invention is produced in one piece in an injection molding process, wherein the disk-shaped main body and the blades formed thereon are made of hard materials. With respect to the direction of rotation of the grinding element in use, the individual blades are arranged immediately behind a usually cylindrical opening in the main body such that the rake face of the respective blade immediately adjoins the wall of the opening and runs in the direction of the extension of said opening such that the rake angle is formed. A rake angle of α=0° or a positive or negative rake angle can be set very easily, the limits thereof being such that when the rake face has a partially conical shape, the following applies: −30°≦α≦30°.

A particularly favorable arrangement that allows the best possible cutting effect to be achieved is obtained with a grinding element in which the openings are arranged, with their respective axes, on a first curve, which, seen from a starting point adjacent to the center axis to an outer end, has the shape of a spiral; in which the first curve has the shape of an Archimedean spiral; and in which the first curve has the shape of a spiral with a progressive pitch towards the outer end as the blades have a smaller radial offset with respect to the blade arranged therebehind or in front thereof The further development of the grinding element such that openings are provided that are arranged on a second curve adjoining the outer end of the first curve and extending in the shape of a partial spiral across less than a circumference of the main body and/or such that openings are provided that are arranged on an outer circular curve forms the transition towards the outer edge of the grinding element.

The further development of the grinding element such that openings arranged immediately adjacent to each other on the at least one curve have identical distances a from each other optimizes the above advantages.

The further development of the grinding element such that—in relation to an x-y-z coordinate system the z-axis of which is congruent with the axis of a respective opening and the y-axis of which runs through the center axis and the axis of the respective opening, in other words radially to the center axis, and the x-axis of which runs perpendicularly to the y-axis and to the z-axis—the cutting edge extends, in relation to the x-axis, outwardly across an angle γ and inwardly across an angle β, wherein 0°≦γ≦45° and 0°≦β≦45°, and/or such that the blades taper towards a rear end section in a direction counter to the direction of rotation, and the respective end section is arranged on the main body in a position opposite to the respective x-axis and inwardly offset towards the center axis ensures that the blades come in contact with the material to be cut only with their cutting edges so there is no or virtually no friction at the side flanges of the blades. Furthermore, this allows the material, which is removed in the cutting process, of the workpiece to be machined to run off smoothly across the rake face.

An optimum height of the blades above the main body is obtained by the configuration in which the blades have a height b above the main body, wherein 0.1 mm≦b≦10 mm.

The particularly favorable materials for producing the grinding element is crystalline hard material, wherein the blades and the main body consist of a hard material in the form of Al₂O₃ or ZrO₂ or Si₃N₄ or SiC or of a hard metal, in particular WC—Co; the optimum grain size k of the sintered hard material is such that 0.1 μm≦k 15 μm.

The gist of the particularly favorable method for producing a grinding element according to the invention is that the grinding element is produced virtually in one process step by injection molding from an initial material produced by mixing and kneading from an organic binding agent that becomes moldable when heated and hard material in the form of particles. In this process, the grinding element is already molded substantially into its final shape, consisting of a usually disk-shaped main body, the openings and the blades. After removing the raw component, produced by injection molding, from the mold, the binding agent is removed by means of a solvent and/or thermally, in other words under the influence of heat. Afterwards, the raw component is sintered, thus ensuring that the grinding element obtains its final hardness.

The hard material used is in the form of particles of Al₂O₃ or ZrO₂ or Si₃N₄ or SiC or hard metal, in particular WC—Co while the binding agent used is in the form of organic high polymers such as polyolefins, polyamides or polyacrylates. According to one aspect of the method, the binding agent is removed from the raw component by means of heat and/or solvents. When the binding agent is removed under the influence of heat, this takes place under the following conditions: when using Al₂O₃ or ZrO₂ or Si₃N₄ or WC—Co particles at a temperature of 510° C. in the presence of ambient air, and when using SiC particles at a temperature of 280° C. to 1000° C. in an inert gas atmosphere or under vacuum. Sintering takes place under the following conditions when using:

Al₂O₃ and ZrO₂: 1300° C. to 1700° C. under atmosphere, without pressure;

SiC: 1900° C. to 2200° C. in an argon inert gas atmosphere, without pressure;

Si₃N₄: 1600° C. to 1800° C. in a nitrogen inert gas atmosphere, 7 to 50 bar;

WC—Co: 1250° C. to 1500° C. in an argon inert gas atmosphere, 1 to 50 bar

The injection-molding tool used in particular to mold the grinding element into its final shape is configured such that two tool components are provided that define a molding space when the injection-molding tool is closed. Bolts are arranged on one tool component for molding the openings and the rake faces, the bolts engaging drill holes of the other tool component when the injection-molding tool is closed. Furthermore, recesses are formed in one tool component for molding the blades.

Further features, advantages and details of the invention will be apparent from the ensuing description of an exemplary embodiment, taken in conjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a schematic view of an injection-molding tool for producing a raw component of a grinding element according to the invention;

FIG. 2 shows a plan view of a molding plate of the injection-molding tool according to FIG. 1;

FIG. 3 shows a partial section through the tool according to section line III-III in FIG. 2;

FIG. 4 shows the arrangement of bolts on the tool upper part;

FIG. 5 shows a partial cross-section through a grinding element according to the invention, comprising blades with a partially cylindrical rake face;

FIG. 6 shows a plan view of the blade with the first curve in the shape of a spiral with a progressive pitch towards the outer end, with an opening being arranged in the grinding element in such a way as to precede said blade;

FIG. 7 shows a plan view illustrating the position of the blade in relation to the opening preceding said blade;

FIG. 8 shows a plan view of a blade with a partially conical rake face and the opening being arranged such as to precede said blade;

FIG. 9 shows a cross-section through the cutting edge according to FIG. 8 according to section line IX-IX in FIG. 8;

FIG. 10 shows a plan view of a blade with a partially conical rake face that differs from that shown in FIGS. 8 and 9 and the opening arranged such as to precede said blade; and

FIG. 11 shows a cross-section according to section line XI-XI in FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A grinding element 1 in the manner of a grinding wheel, which will be described in more detail below, is produced by injection molding in an injection-molding tool 2, which is only shown in a schematic view. Said injection-molding tool 2 comprises a tool lower part 3 and a tool upper part 4 that are in engagement with each other when the tool 2 is closed. The tool upper part 4 is composed of two parts, comprising an inner molding plate 4′ and an upper closing plate 4″. When the injection-molding tool 2 is closed, the lower part 3 and the molding plate 4′ together define a molding space 5 in which the grinding element 1 is molded by injection molding. Seen in a plan view, the molding space 5 is circular and has a center axis 6. In the tool upper part 4, an inlet 7 is provided for an injection molding material 8 to be injected by means of an injection molding machine, said inlet 7 running concentrically to said axis 6.

A plurality of bolts 9 are fastened in the tool upper part 4 in such a way as to face the molding space 5, with a corresponding drill hole 10 in the tool lower part 3 and a drill hole 10′ in the molding plate 4′ being associated to a respective bolt 9 in such a way that when the injection-molding tool 2 is closed, a respective bolt 9 passes through in each case one drill hole 10′ and engages in each case one drill hole 10, as outlined in FIG. 3.

In the surface 11 of the molding plate 4′ facing the molding space 5, recesses 12 are formed in such a way as to face a respective bolt 9, the recesses 12 being described in more detail below.

As can be seen from FIG. 4, the axes 13 of the drill holes 10 and 10′, and therefore of the bolts 9, lie on an Archimedean spiral or on a spiral having a first curve 14 with a progressive pitch such that the radius thereof increases from an inner starting point 15 of said first curve 14 to the outer end 16 thereof from a radius R1 to a radius R2. From said end 16, a short section of a degressive second spiral curve 17 extends across approximately half a circumference, in any case across less than a full circumference. On the outside, drill holes 10 and corresponding bolts 9 are arranged on a circular curve 18 as well, with the axis 6 serving as center axis.

The distance a of the drill holes 10 arranged on a particular curve, in other words the first curve 14, the second curve 17 and the curve 18, from each other is identical for all drill holes 10, 10′.

The shape of the recesses 12 in the inner surface 11 of the molding plate 4′ will be explained indirectly by means of FIGS. 5 and 6. Each of these Figures shows a partial section of a grinding element 1 molded in the injection-molding tool 2 from the injection molding material 8, the grinding element 1 comprising a blade 19 the shape of which corresponds to the respective recess 12 closed by in each case one bolt 9. The blade 19 has a partially cylindrical or partially conical rake face 20 with a rake angle −30°≦α≦30° that is concentric to the axis 13 of the bolt 9 or the drill hole 10 and corresponds to the circumferential surface of the bolt 9. In order to produce a rake angle α=0° shown in FIG. 5, the section 9′ of the bolt 9 arranged in the recess 12 is cylindrical. In order to produce a rake angle α≠0, said section 9′ of the bolt 9 is conical. If the section 9′ tapers in a direction away from the tool lower part 3, then the bolt 9 needs to be arranged in the tool lower part 3 to ensure that the grinding element 1 is easily removable from the mold.

The blade 19 has a wedge angle β such that 30°≦β≦120°. The blade 19 has a rounded end section 22 with a radius r2 that is smaller than the radius r1 of the respective drill hole 10 or of the bolt 9. Side flanks 23, 24 protrude from said rake face 20 towards said end section 22, as can in particular be seen in FIG. 6. In other words, the blade 19 tapers towards the end section 22. The blade 19 has a height b above the main body 25 of the grinding element 1, said height b being at the same time the height above a cylindrical opening 26 produced by the respective bolt 9 in the disk-shaped main body 25 of the grinding element. In other words, the partially cylindrical or partially conical rake face 20 directly adjoins said opening 26.

As can further be seen from FIGS. 5 and 6, a cutting edge 27 is formed by the intersection of the rake face 20 and the back (flank) 21 of the blade 19, wherein said cutting edge 27 is offset outwardly with respect to the first curve 14 or the second curve 17 or the circular curve 18. In FIG. 7, this is shown in an x-y-z coordinate system the y-axis of which passes through the respective axis 13 of a drill hole 10, and therefore through the opening 26 and the center axis 6 of the grinding element 1. The x-axis is perpendicular thereto and to the axis 13. The z-axis, which is only outlined in FIG. 5, is congruent with the respective axis 13 of an opening 26. In FIG. 7, the boundary lines of the side flanks 23, 24 of the blade 19 are shown in the plane of the main body 25, as is outlined in FIG. 5 as well. In this plane, from which the blades 19 protrude, the side flanks 23, 24 intersect the boundary line, i.e. the wall 28, shown in the shape of a circle, of the opening 26. Half lines r23 or r24 extending from the respective axis 13 towards these intersection points or corner points 23′ or 24, respectively, form an angle γ or δ, respectively, with the x-axis. With respect to the center axis 6, the angle γ is the angle that is associated to the outer side flank 23 of the blade 19. The angle δ is the angle that is associated to the side flank 24 of the blade 19 facing the center axis 6, with 0°≦γ≦45°, and 0°≦δ≦45°.

If α<0, the wall 28 of the opening 26 and the cutting edge do not coincide in the plan view as shown in FIGS. 6 and 7 for a partially cylindrical rake face 20. It shall be noted that in this case, i.e. if α<0, the graphic representation of the cutting edge 27 must be drawn from the wall 28 of the opening 26 back into the back (flank) 21 of the blade 19 as shown in the illustration according to FIGS. 8 and 9. Alternatively, if α>0, the cutting edge 27 is curved from the wall 28 of the opening 26 towards the latter, as can be seen from FIGS. 10 and 11. In FIGS. 8 and 11 showing partially conical designs of the rake faces 20 with cutting edges 27, the same reference numerals were used as for the partially cylindrical design of the rake faces 20 with cutting edges 27 described above to ensure clarity of the description.

If the two angles γ and δ are not the same, a cutting edge 27 is obtained that runs obliquely to the cutting speed vector formed by the x-axis to reduce dynamic cutting forces caused when the cutting edge 27 penetrates into a material to be ground. This design ensures that the cutting edge 27 penetrates into said material particularly smoothly. As will be apparent from the above description with reference to FIG. 7, the end section 22 is offset inwardly with respect to the x-axis, in other words the cutting speed vector, in such a way that a collision of the side flanks 23 or 24 of the blade 19 with a workpiece during cut formation is safely prevented. As can in particular be seen from FIG. 2, the respective opening 26 is arranged—with respect to the direction of rotation in the cutting process—in such a way as to precede the cutting edge 27 and the rake face 20 of the associated blade 19, allowing chips to be carried away through said opening 26.

It is worth repeating that the recesses 12 and the respective section 9′ of the bolts 9 virtually form the negative image of the blade 19.

The grinding element is produced as follows:

In order to prepare the actual injection molding process as already mentioned above, a so-called feed stock, in other words an initial material is produced. Said initial material contains organic binding agents that will become moldable or injection-moldable when heated. Organic binding agents of this type are high polymers such as polyolefins, polyamides or polyacrylates and suitable softeners such as phthalates, paraffins or polyethylene glycols added to reduce the melt viscosity. In a next step, a hard material in the form of particles is admixed to these organic binding agents, wherein said particles are either Al₂O₃ or ZrO₂ or Si₃N₄ or SiC particles, or tungsten carbide particles coated with cobalt. From the high polymers and the hard material particles, the so-called feed stock is produced in an extruder by mixing and kneading. In this process, the hard material particles are dispersed in the high polymers.

In a subsequent working step, the initial material is heated in an injection molding machine and injected into the injection-molding tool 2 where the main body 25 is molded to obtain the numerous blades 19, which are formed and arranged in accordance with the above description, and openings 26, which are in each case associated to a respective one of the blades 19. After removing the injection-molded grinding element 1, in other words the raw component, from the mold, the organic binding agents of said raw component, are removed using conventional solvents and/or by means of a heat treatment. When using Al₂O₃ or ZrO₂ or Si₃N₄ or WC—Co particles, the solvents are removed at a temperature of 510° C. and in the presence of ambient air.

When using SiC particles, the binding agents are removed in an inert gas atmosphere or under vacuum at a temperature of 280° C. to 1000° C. The temperature is selected depending on the residual strength the injection molded component needs to have for further use after removing the binding agents. If said heat treatment for removing the binding agent would destroy the raw component or make it too brittle, the binding agent is removed essentially or entirely using suitable conventional solvents.

After removing the binding agent, the raw component is sintered under the following operating conditions:

Al₂O₃ and ZrO₂: 1300° C. to 1700° C. under atmosphere without pressure;

SiC: 1900° C. to 2200° C. in an argon inert gas atmosphere without pressure;

Si₃N4: 1600° C. to 1800° C. in a nitrogen inert gas atmosphere, 7 to 50 bar;

WC—Co: 1250° C. to 1500° C. in an argon inert gas atmosphere, 1 to 50 bar.

During the sintering process, the particles combine to form one body, the grinding element 1, by solid state diffusion, said grinding element 1 having grain sizes k of 0.1 μm≦k≦15 μm.

During the sintering process, the respective blade 19 will substantially retain the shape it has obtained during injection molding. The rake face 20 was molded by the section 9′ of the respective bolt 9. The remaining shape of the blade 19 was molded by the corresponding shape of the recess 12. 

1-23. (canceled)
 24. A grinding element consisting of a disk-shaped main body and cutting elements formed as a unit therewith, wherein the main body and the blades are made of sintered hard material, wherein, in relation to a direction of rotation of the grinding element about a center axis, each blade is immediately preceded by an opening passing through the main body , and wherein each blade has a rake face having one of the group comprising a partially cylindrical shape with a rake angle α=0° and a partially conical shape with a rake angle α≠0°.
 25. A grinding element, wherein when the rake face has a partially conical shape, the following applies: −30°≦α≦30°.
 26. The grinding element according to claim 24, wherein the openings are arranged, with their respective axes, on a first curve, which, seen from a starting point adjacent to the center axis to an outer end, has the shape of a spiral.
 27. The grinding element according to claim 26, wherein the first curve has the shape of an Archimedean spiral.
 28. The grinding element according to claim 26, wherein the first curve has the shape of a spiral with a progressive pitch towards the outer end.
 29. The grinding element according to claim 26, wherein openings are provided that are arranged on a second curve adjoining the outer end of the first curve and extending in the shape of a partial spiral across less than a circumference of the main body.
 30. The grinding element according to claim 25, wherein openings are provided that are arranged on an outer circular curve.
 31. The grinding element according to claims 24, wherein openings arranged immediately adjacent to each other on the at least one curve have identical distances a from each other.
 32. The grinding element according to claim 24, wherein, in relation to an x-y-z coordinate system the z-axis of which is congruent with the axis of a respective opening and the y-axis of which runs through the center axis and the axis of the respective opening, in other words radially to the center axis, and the x-axis of which runs perpendicularly to the y-axis and to the z-axis, the cutting edge extends, in relation to the x-axis, outwardly across an angle γ and inwardly across an angle β, wherein: 0°≦γ<45° and 0°≦β≦45°.
 33. The grinding element according to claim 24, wherein the blades taper towards a rear end section in a direction counter to the direction of rotation, and wherein the respective end section is arranged on the main body in a position opposite to the respective x-axis and inwardly offset towards the center axis.
 34. The grinding element according to claim 24, wherein the blades have a height b above the main body (25), wherein 0.1 mm≦b≦10 mm.
 35. The grinding element according to claim 24, wherein the hard material is crystalline.
 36. The grinding element according to claim 24, wherein the blades and the main body consist of a hard material in the form of one of the group comprising Al₂O₃ and ZrO₂ and Si₃N₄ and SiC and a hard metal.
 37. The grinding element according to claim 36, wherein said hard metal is WC—Co.
 38. The grinding element according to claim 24, wherein the sintered hard material has a grain size k, wherein 0.1 μm≦k 15 μm.
 39. A method for the production of a grinding element consisting of a disk-shaped main body and blades formed as a unit therewith, wherein the main body and the blades are made of sintered hard material, wherein, in relation to a direction of rotation of the grinding element about a center axis, each blade is immediately preceded by an opening passing through the main body, and wherein each blade has a rake face having one of the group comprising a partially cylindrical shape with a rake angle α=0° and a partially conical shape with a rake angle α≠0°, wherein an initial material is produced by kneading and mixing from an organic binding agent that becomes moldable when heated and hard material in the form of particles, wherein, in a subsequent step, a raw component of the grinding element is produced by injection molding, wherein, in a subsequent step, the binding agent is removed from the 20 raw component, and wherein, in a subsequent step, the grinding element is formed from the raw component in a sintering process.
 40. The method according to claim 39, wherein the hard material used is in the form of particles of one of the group comprising Al₂O₃ and ZrO₂ and Si₃N₄ or and SiC and hard metal.
 41. The method according to claim 40, wherein said hard metal is WC—Co.
 42. The method according to claim 40, wherein the following organic high polymers are used as binding agent: one of the group comprising polyolefins, polyamides and polyacrylates.
 43. The method according to claim 40, wherein the binding agent is removed from the raw component by at least one of the group comprising heat and solvents.
 44. The method according to claim 43, wherein the binding agent is removed by application of heat under the following conditions: when using one of the group comprising Al₂O₃ and ZrO₂ and Si₃N₄ and WC—Co particles at a temperature of 510° C. in the presence of ambient air, and when using SiC particles at a temperature of 280° C. to 1000° C. in one of the group comprising an inert gas atmosphere and vacuum.
 45. The method according to claim 40, wherein sintering takes place under the following conditions when using: Al₂O₃ and ZrO₂: 1300° C. to 1700° C. under atmosphere, without pressure; SiC: 1900° C. to 2200° C. in an argon inert gas atmosphere, without pressure; Si₃N₄: 1600° C. to 1800° C. in a nitrogen inert gas atmosphere, 7 to 50 bar; and WC—Co: 1250° C. to 1500° C. in an argon inert gas atmosphere, 1 to 50 bar.
 46. An injection-molding tool for the production of the grinding element consisting of a disk-shaped main body and blades formed as a unit therewith, wherein the main body and the blades are made of sintered hard material, wherein, in relation to a direction of rotation of the grinding member about a center axis, each blade is immediately preceded by an opening passing through the main body, and wherein each blade has a rake face having one of the group comprising a partially cylindrical shape with a rake angle α=0° and a partially conical shape with a rake angle α≠0°, using a method wherein an initial material is produced by kneading and mixing from an organic binding agent that becomes moldable when heated and hard material in the form of particles, wherein, in a subsequent step, a raw component of the grinding member is produced by injection molding, wherein, in a subsequent step, the binding agent is removed from the raw component, and wherein, in a subsequent step, the grinding member is formed from the raw component in a sintering process, wherein two tool components are provided that define a molding space when the injection-molding tool is closed, wherein bolts are arranged on one tool component for molding the openings and the rake faces, the bolts engaging drill holes of the other tool component when the injection-molding tool is closed, and wherein recesses are formed in one tool component for molding the blades.
 47. The injection-molding tool according to claim 46, wherein one tool component is formed in two pieces with the molding plate defining the molding space, wherein the molding plate comprises the recess for molding the blades and drill holes penetrated by the bolts.
 48. The injection-molding tool according to claim 46, wherein the bolts are have one of the group comprising a cylindrical and a conical shape in the region of the recess. 